Control circuits



April 17, 1956 l. GROSS 2,742,595

CONTROL CIRCUITS Filed Dec. 8, 1952 9YIII' 12% 9l L A) OMA l iPROTECTED CIRCUIT g 87 50 3: PROTECTED P CIRCUIT d C 5OWYPROTECTED g CIRCUIT \llll D; PROTECTED CIRCUIT FUSE ALARM RELAY l8 m 1 RROTECTWE MEANS FIG. 3 L J H l A ulfil A, (+\OOv) (wow) i i5 5 l E I I 5 F; 19 1 K 8., (+50v) (+5 I 4 i 0v) 5 1 H E g (C 1 25K 1 (-V) 51 3 (75 5" a 8 E D $9 37.5 K D (-noov) E (-IOOV) E L 1 l8 INVENTOR i ISADORE GROSS 2O FUSE BY 4\ ALARM RELAY TJ W 6?. M

ATTO NEY United States Patent CONTROL CIRCUITS Isadore Gross, Philadelphia, Pa., assignor to Brirronghs Corporation, Detroit, Mich., a corporation of Michigan Application December 8, 1952, Serial No. 324,686

4 Claims. (Cl. 317-46) This invention relates to electrical control systems and particularly to systems in which individual fuses are employed for different circuits of a system and wherein control relay means is provided to protect delicate instruments or tubes in event of fuse failure in any one of the fused circuits.

Because the load conditions of several electrical circuits connected to a single power supply and the time delay requirements for protective devices connected in the several circuits may be different, it is desirable to separately fuse dilferent circuits in accordance with the most desirable protection parameters. When the circuits are separately fused, however, the failure of one fuse may remove bias potentials from tubes or otherwise cause too much current to flow in other types of delicate instruments. Accordingly, an associated relay or similar circuit opening means is desired to atfordproper protection where needed by removing the potential from those circuits requiring protection or otherwise actuating protective circuits.

Three-terminal safety type fuses are available in the art which may be adapted to connect one fuse terminal to an alarm bus when the fuse fails to actuate a relay operated alarm system as described in the copending application of Isadore Gross entitled Control Systems, Serial No. 317,938 filed October 31, 1952 and assigned to the same assignee as this application, now Patent No. 2,707,779. It has, in the past, been difficult to actuate a relay in response to failure of one of a group of standard two-terminal fuses and the three-terminal safety type fuses are generally not suitable for use with standard twoterminal insulated fuse posts and may subject an operator to shock hazard upon replacement.

To obtain the maximum protection in the minimum time, a relay is selected that will respond quickly. It is generally desirable to provide a corresponding relay actuation network circuit for obtaining fast response of the ice utilizing a control relay circuit causing the control relay to be actuated by a current change through the relay winding due to fuse failure in any one of several fused circuits.

Other objects and features of advantage of the present invention will be found throughout the following more detailed description of the invention particularly when considered in connection with the accompanying drawings; in which:

Fig. l is a schematic circuit diagram showing the operation of a simplified embodiment of the invention;

Fig. 2 is a schematic circuit diagram of a control circuit showing a further embodiment of the invention; and

Fig. 3 is a schematic circuit diagram of another control circuit.

Throughout the drawings like reference characters will be used to designate like circuit elements to facilitate comparison.

Referring now in particularity to Fig. 1, a circuit interrupting device such as a fuse 10 is shown in a direct current line A, with an impedance network made up of current determining resistor 12, and relay means 14. The voltage source in this case comprises the battery 9 which also supplies energy to the protected circuit 11. The relay means has its relay coil 18 de-energized by a current change caused by failure of fuse 10, whereby the relay contact 20 is operated to actuate the control circuit 8.

The circuit of Fig. 2 shows an embodiment whereby each protected circuit of the group 1111"', inclusive, is supplied 100 volts from the power supply source 9.

I Each of the power supply leads A, B, C and D to the relay upon fuse failure in any one circuit by the selection of proper circuit parameters to maintain at a minimum any time lag between the fuse failure and the relay operation. Also in the interest of circuit economy, it is desirable to provide a single control relay operable by fuse failure in any one of several fused circuits.

It is, therefore, a general object of the invention to provide improved electrical control systems.

It is another object of the invention to provide an improved control system operable upon failure of a standard two terminal fuse.

It is still another object of the invention to provide improved control systems with a single relay protective device.

It is a further object of the invention to provide an improved control circuit for separately protected circuits, actuated by fuse failure in any one of a plurality of power supply leads, to disconnect other power supply leads from the protected circuits.

In accordance with the teachings of the present invention, there is, therefore, provided a fused alarm system protected circuits includes a separate fuse 10. An impedance network 13, comprises a branched circuit having each branch thereof connected to a supply lead between the protected circuit and the fuse. The network 13, includes a plurality of current proportioning resistors 15, 15, etc. respectively connected in the several branches thereof, said branches having a common junction at the distribution bus 16. The relay coil 18 is connected in a common portion of the branched network circuit between the distribution bus and ground, which represents a common reference potential for similar poles of the protected circuits and the volt source and the protective means is actuated by changes of current through the coil.

T-he relay'comprising coil 18, operates on a marginal basis. In this case it has been selected to attain one operating state with 20 milliamperes and the other when the current falls to 15 milliamperes. The network has been proportioned to maintain 2O milliamperes through the relay coil under normal operating conditions when all fuses are intact. Neglecting the impedance of the relay coil 18, each resistive branch of the network has a resistance of 20,000 ohms and therefore passes 5 milliamperes of current from the 100 volt source as long as the fuse is intact. Therefore, it is readily seen that upon fuse failure in any one supply line the current through the relay coil will drop to 15 milliamperes and the relay contact 20, will then actuate the protective means.

The load required by each protected circuit has been selected to illustrate the adaptability of the present invention to systems requiring long and short time delays in fuse failure for various circuits. The circuit connected to the lead A, has been selected to require 10 milliamperes, the one connected to lead B, 50 milliamperes, the one connected to lead C, 50 milliamperes and to lead D, 100 milliamperes. It is readily seen that fuses selected for protection of supply leads A and D would differ due to the load requirements. Taking, for example, supply leads B and C, where the load current requirements are identical, it is foreseeable that the type of equipment to be protected in each circuit would be radically different so as torequire afast operating'fuse in one and a slow operating oneir'i'the other. Theaters, the disadvantage of having a simple protective'fuse for several circuits requiring the same potential or current isreadily apparent. However, the protective relay is actuated by failure of any one fuse to afford greater overall'protection in accordance with the present invention. fl

A circuit as shown in Fig. 3, which likewise has a plurality of differently fused circuits, is an embodiment wherein the power supply 9, is disconnected from the protected electrical circuit 11, upon a change of current through the relay coil, 18, which results in opening contact 20. The power supply leads A, B, C and D have potentials both. positive and. negative with respect to the ground potential leadE, and eachsupply lead is connected to. theprotected circuit 11, through a separate fuse 10. A branched resistive network 13, made up of a plurality of current proportioning resistors 15, 15, etc. is connectedtoeach leadbetween the protected circuit and the fuse, each resistor being individual to one ofthe branches respectively connected to the supply leads. A distribution bus 16, which provides a-comrnon' junction for the several resistive branches of the network, electrically connects the fuse alarm relay coil with each of the resistors. The relay coil is therefore arranged in a common portion of the circuit between the junction of the several branches and ground. The resistive network is designed to maintain the voltage across the relay coil at zero potential by establishing a current balance in the network during normal operation to keep lead 16, at zero potential.

' To illustrate the operation ,of the relay, the following circuit parameters have been selected in the typical cir-' cuit shown:

the combination of voltage means having a terminal there: armantsifiea at a reference potential, a group of protected circuits each having one terminal thereof at said reference potential, individual circuit means supplying voltage to said protected circuits from said voltage means, each comprising a lead connecting a terminal of a protected circuit other than said oneterminal with a terminal of the supply maintained at other than reference potential and including circuit interrupting means serially connected therein, a branched network having the branches thereof respectively connected 'to said several leads intermediate an interrupting means and a protected circuit and having a common portion connecting the junction of said branches witha terminal at reference potential, resistors individual to said branches, and a relay having the operating winding thereof serially connected in said common portion of the network for marginal operation of the relay responsive, respectively, to a normal value of the current in said winding determined by an uninterrupted condition of all said leads and a current value selectively departing therefrom, said relay controlling protective means for the protected circuits.

2. In means for protecting the remainder of the circuits of a group commonly connected to a source of A; volts +100 B do C do -75 j D --d0. I E do w 0 R15 ..ohrns 50,000 R15 f do 25,000 R15" do 37,500 R15 do 50,000

The relay is energized by 1 milliampereof current, and 2 milliamperes of bleeder-current pass through-each resistor during normal conditions. The 1 milliampere -of current was selected for the relay so that it will be as sensitive as possible andthereby actuate its contact 20, in a minimum of time. Therefore, it is readily seen that due to the fuse failure in any one supply line,- the current to oneof the branches of the network will be cut off resulting inan unbalance of current in the relay coil of about 2 milliamperes. The current unbalance, being greater than 1 milliampere, will actuate the relay contact and in this case remove the power from each lead of the protected circuit. .This is done by connecting relay contact 20, in the supply lead to the power supply 9. It is, therefore, clear from the foregoing description that the present invention by providing an electrical control system, wherein a single relay is operable by current change effected by the failure of one of a plurality of two terminal fuses, has improved the state of the art sothat circuit economy and fast protective action may be realized along with the many other features of advantage. -Having therefore described detailed embodiments of the invention, setting forth its organization and its mode of operation, those features believed descriptive of the nature of the invention are defined withparticularity in the appended claims. I What is claimedisz, .7 1. In means .for protecting the remainder of the circuits of a group commonlyconnected to voltage means as to one, pole thereof in the event of the interrupt-ion of the supply of voltageto one ormore circuits of the group voltage as to one pole thereof in the event of the interruption of. the supply of voltage to one or more circuits of the group due to overload the combination of a source of .voltage, a group of protected circuits, common conducting means directly connecting each protected circuit with the source as to one pole thereof and individual circuit vmeans connecting each protected circuit with the source asto the -other polethere, said individual means eachcomprising a lead having circuit interrupting means connected thereinadapted to disconnect the protected circuit from the source of voltage responsive to overload, abranched networkhaving the branches thereof respec-. tively connected to said several leads intermediate an interrupting meansand a protected circuitand having a commonportion connecting the junction of said branches with a.terminal atthe potential of said one pole of the protected circuits, resistors individual to said branches,- and a relay having the operating winding thereof connected in, the common portion of said network for mar ginal operation of the relay responsive, respectively, to a normal value ofthe current in said winding determined by an uninterrupted condition of all said leads and a current value selectively departing therefrom, said relay controlling protective means for the protected circuits.

3,. In means for protecting the remainder of the circuits of a group commonly connected to a common terminal of plural sources of voltage as to one pole thereof in the event of, theinterruption of the supply of voltage to one ormorecircuits of the group the combination of aplurality. of voltage sources having a common terminal main tained at a reference potential, a' group of protected circuits having a common terminal conductively maintained at saidreference potential, individual circuit means connecting said protected circuits with said sources each comprising a lead connecting a non-common terminal of a protected circuit with a terminal of a source maintained at other than reference potential and including circuit interrupting means therein, a branched network having the branches thereof respectively terminally connected to said leads intermediate an interrupting means and a protected circuit and having a" common portion connecting the junction of the branches with a terminal at reference'pote'n'ti'al, resistors individual to said branches, and a relay having the operating winding thereof connected in said common portion of the control circuit'for marginal operation of the relay responsive, respectively, to a normal value of the current in said winding determined by an uninterrupted condition of all said leads and a current value selectively departing therefrom, said relay controlling protective means for the protected circuits.

4. The-combinationdefined in claim 3 wherein said protective means for the protected circuits includes means simultaneously deactivating said plural sources of voltage upon operation of said relay under the second of said defined conditions.

References Cited in the file of this patent 6 Suger Sept. 16, 1930 Schelling Aug 4, 1931 Cousins Feb. 14, 1939 Jones Aug. 19, 1952 Dion et a1. Oct. 19, 1954 

